1. Field of the Invention
The present invention relates to polyol ether derivatives which are useful as polar oils, organic solvents, lubricants, synthetic lubricating oils, or refrigeration oils, or as intermediates in the production of the above oils, etc.; and to a method for producing the polyol ether derivatives; and also to a working fluid composition for a refrigerating machine using the above polyol ether derivatives as a base oil. Here, the term "polyol ether" means a partially etherified polyol.
2. Discussion of the Related Art
Recently, the use of dichlorodifluoromethane (CFC12) for refrigerators and car air conditioners has been restricted, and will be legally banned in order to protect the ozone layer. Also, the use of chlorodifluoromethane (HCFC22) for room air conditioners is about to be legally regulated. Thus, hydrofluorocarbons which do not destroy the ozone layer, such as 1,1,1,2-tetrafluoroethane (HFC 134a), difluoromethane (HFC32), and pentafluoroethane (HFC125), have been developed as substitutes for CFC12 or HCFC22.
However, since the polarity of hydrofluorocarbons is higher than that of CFC12 or HCFC22, the use of conventional lubricating oils, such as naphthenic mineral oils, poly-.alpha.-olefins, or alkylbenzenes, causes two-layer separation of the working fluid at low temperatures. This is due to poor compatibility between the conventional lubricating oils and hydrofluorocarbons. Two-layer separation hampers oil return, which in turn interferes with heat transfer due to deposition of a thick oil film on a heat transfer surface of the condenser and evaporator used as heat exchangers. It can also cause significant failures, such as poor lubrication, and foaming upon starting operation. Therefore, the conventional refrigeration oils cannot be used as refrigeration oils under these new refrigerant atmospheres.
As for lubricity, CFC12 and HCFC22 generate hydrogen chloride upon partial decomposition. The hydrogen chloride thus formed reacts with the friction surface to form a coating of chlorides, thereby improving the lubricity. On the other hand, non chlorine containing hydrofluorocarbons are not expected to have such an effect; therefore, refrigeration oils used in combination with hydrofluorocarbons are required to have a further excellent lubricity when compared to the conventional refrigeration oils.
In addition, the refrigeration oils used in combination with hydrofluorocarbons have to have good thermal stability in the presence of hydrofluorocarbons.
Moreover, with compression-type refrigerating machines for electric refrigerators and air conditioners, since organic materials are used for motor components, such as insulators and enameled wires, the working fluid comprising a hydrofluorocarbon and a refrigeration oil is required to have no adverse effects on these organic materials and also have a good insulating property.
Refrigeration oils which can be used in combination with hydrofluorocarbons, such as 1,1,1,2-tetrafluoroethane (HFC134a), disclosed in U.S. Pat. No. 4,755,316 and Japanese Patent Laid-Open No. 2-129294, are ether compounds of polyalkylene glycols (hereinafter abbreviated as PAG-OH) prepared by the addition of an alkylene oxide to a polyhydric alcohol which is not alkyl-capped at the terminal hydroxyl. As an example of the polyhydric alcohols used, the former discloses trimethylol propane and the latter discloses glycerol.
In order to solve various problems of the above compounds, such as poor compatibility with HFC and high hygroscopicity, compounds prepared by alkyl-capping the terminal hydroxyl groups of the above ether compounds (hereinafter abbreviated as PAG) are disclosed in Japanese Patent Laid-Open Nos. 3-14894, 3-205492, 4-20596, 4-359996, and 5-98275.
Since PAG-OH and PAG have a higher polarity than the naphthenic mineral oils, their compatibility with HFC134a at low temperatures is good. However, PAG-OH and PAG phase-separate as the temperature increases as mentioned in U.S. Pat. No. 4,755,316. There are also several problems with these compounds. For example, a poor insulating property is one of the problems. Due to this significant problem, PAG-OH and PAG cannot be used for a refrigerating device of electric refrigerators and air conditioners where a motor is incorporated in a compressor. Therefore, applications of PAG-OH and PAG are proposed for car air conditioners where their poor insulating property does not cause any problems. High hygroscopicity is another significant problem of PAG-OH and PAG. The water absorbed by the compounds causes thermal instability of the compounds in the presence of HFC134a, and hydrolysis of organic materials, such as PET films.
In order to solve the above problems of polyether compounds, such as poor insulating property and high hygroscopicity, ester compounds and carbonate compounds have been developed. For example, mixed oils of polyether oils and ester oils are disclosed in U.S. Pat. No. 4,851,144 (corresponding to Japanese Patent Laid-Open No. 2-276894) and Japanese Patent Laid-Open No. 2-158693; ester oils are disclosed in Japanese Patent Laid-Open Nos. 3-505602, 3-128991, and 3-128992; and carbonate oils are disclosed in Japanese Patent Laid-Open Nos. 2-132178 and 3-149295, and European Patent No. 421,298. All of the compounds disclosed can be used as a refrigeration oil in combination with 1,1,1,2-tetrafluoroethane (HFC134a).
Ester compounds and carbonate compounds show good compatibility with hydrofluorocarbons and high thermal stability in the presence of hydrofluorocarbons. Also, these compounds have markedly better insulating properties and much lower hygroscopicity than polyether compounds.
However, when compared with the conventional CFC12-mineral oil working fluid system, both freon and oil tend to have a high polarity in the hydrofluorocarbon-ester oil system or hydrofluorocarbon-carbonate oil system, and the systems become highly hygroscopic. Particularly, in the system using an ester oil, a carboxylic acid is likely to be formed owing to hydrolysis of the ester oil, and the formed carboxylic acid may in turn corrode and wear down the metals. Also, in the case of using a carbonate oil, there arises such a problem that a non-condensable carbon dioxide gas is generated owing to hydrolysis of the carbonate oil to cause a low refrigerating capacity.
In particular, in the case of room air conditioners, it is common practice to fill an air conditioner with a refrigerant upon installation. Therefore, unlike refrigerating machines for which filling of refrigerant is carried out in a factory, it is almost impossible to prevent a working fluid of room air conditioners from being contaminated with water. Therefore, there has been a concern about the reliability of the hydrofluorocarbon-ester oil system and hydrofluorocarbon-carbonate oil system, when used in room air conditioners.
WO93/24435 discloses that a polyvinyl ether compound having good compatibility with hydrofluorocarbons and good insulating property is prepared by polymerization of vinyl ether monomers and subsequent hydrogenation. However, since the polyvinyl ether compound is synthesized by polymerization, it shows molecular weight distribution. Therefore, a part of high molecular weight polymers sometimes causes plugged capillaries of refrigerating machines and worsens the compatibility of the compound with hydrofluorocarbons. Also, the compound requires complicated post-treatment and cannot always be obtained in high yield because the vinyl ether monomers, the starting materials of the polyvinyl ether compound, are not stable substances. In particular, the yield of those with a low degree of polymerization (around 6) is low. Some vinyl ether monomers of certain structures cannot be easily obtained, and are, therefore, very expensive.
As mentioned above, polyvinyl ether compounds show molecular weight distribution. The products with higher molecular weights sometimes cause to impair the performance of the compounds. Polyvinyl ether compounds also have drawbacks of limited availability of the starting materials and poor yields of those with low degrees of polymerization, which together make the product cost expensive.
The refrigerant-oil systems developed so far have various drawbacks as mentioned above. The hydrofluorocarbon-PAG (PAG-OH) oil system has problems in hygroscopicity and insulating property; and the hydrofluorocarbon-ester oil system and the hydrofluorocarbon-carbonate oil system have problems of poor hydrolysis resistance. Both of these systems are unsatisfactory as a working fluid composition for a refrigerating machine, because, as compared with the conventional CFC12-mineral oil system, they have higher hygroscopicity, lower thermal stability, stronger deteriorating action on organic materials, and stronger effects to corrode and wear metals. Polyvinyl ether compounds show a molecular weight distribution and the molecules with high molecular weights cause to lower the compatibility with hydrofluorocarbons. Polyvinyl ether compounds also have drawbacks of limited availability of the starting materials and of high cost.